KR102185741B1 - Analyzing method for thermal behavior of seperate electrode - Google Patents

Abstract

The present invention is to provide an analysis method for separating the thermal behavior of a positive electrode and a negative electrode of a battery, comprising the steps of: preparing a coin cell including a target electrode and a counter electrode; And, it provides a method for analyzing the thermal behavior of individual electrodes, including the step of measuring the thermal behavior of the coin cell by putting the coin cell into a multi-module calorimeter and injecting a current.

Description

Analysis method of thermal behavior of individual electrodes {ANALYZING METHOD FOR THERMAL BEHAVIOR OF SEPERATE ELECTRODE}

The present invention relates to a method for analyzing the thermal behavior of individual electrodes.

As technology development and demand for mobile devices increase, the demand for secondary batteries as an energy source is rapidly increasing. Among these secondary batteries, lithium secondary batteries having a high energy density and voltage, a long cycle life, and a low self-discharge rate have been commercialized and widely used.

As the application fields of lithium secondary batteries are diversified, the requirements for safety of lithium secondary batteries are also increasing. Among the methods of testing the safety of a lithium secondary battery, the overcharge test is to check the temperature change and ignition of the cell while charging the cell with a constant current. Since the temperature change of the cell is a phenomenon that occurs when the temperature change of the positive electrode (NCM three-component system or LCO, etc.) and the negative electrode (graphite, silicon, lithium, etc.) affects complexly, it is necessary to analyze the thermal reaction of only the positive electrode or the negative electrode. It was difficult.

However, since it is possible to improve cell stability through material improvement only when the task of classifying heat generated by the anode or the cathode is prioritized, a method of separating and determining the thermal reactions of the anode and the cathode is required.

Japanese Patent Application Publication No. 2014-022282

In order to solve the above problems, a first technical object of the present invention is to provide a method for analyzing thermal behavior of an electrode, which can separate and analyze only individual thermal behaviors of an electrode to be analyzed, that is, an anode or a cathode.

In one aspect, the present invention comprises the steps of manufacturing a coin cell including a target electrode and a counter electrode; And, it provides a method for analyzing the thermal behavior of individual electrodes, including the step of measuring the thermal behavior of the coin cell by putting the coin cell into a multi-module calorimeter and injecting a current.

According to the present invention, a coin cell is manufactured using a target electrode to be analyzed and a counter electrode made of a material having stable thermal behavior during charging and discharging, and the thermal behavior of the coin cell is measured in a multi-module calorimeter. Only the thermal behavior can be measured separately.

Accordingly, it is possible to separate and analyze the thermal behavior in each of the positive electrode or the negative electrode, and finally, a battery with improved safety can be manufactured using this.

Hereinafter, the present invention will be described in more detail.

The terms or words used in this specification and claims should not be construed as being limited to their usual or dictionary meanings, and the inventor may appropriately define the concept of terms in order to describe his own invention in the best way. It should be interpreted as a meaning and concept consistent with the technical idea of the present invention based on the principle that there is.

The method for analyzing thermal behavior according to an embodiment of the present invention may be performed using a multi module calorimeter (MMC).

The multi-module calorimeter measures the amount of heat and temperature over time while charging and discharging the battery under adiabatic conditions. However, in the case of a multi-module calorimeter, which conventionally manufactures a coin cell including an anode and a cathode to be analyzed and measures the amount of heat and temperature using the same, since the thermal reactions of the target anode and the cathode are combined, the thermal reaction of each electrode is reduced. There was a disadvantage that it could not be judged separately.

Accordingly, the present invention manufactures a coin cell including a target electrode to be analyzed for thermal behavior and a counter electrode made of a material having stable thermal behavior during charging and discharging in order to separate and analyze the thermal reaction at the positive and negative electrodes of the battery. Then, the coin cell was placed in a multi-module calorimeter, and current was injected to measure the thermal behavior of the coin cell.

In this case, the counter electrode is made of a material having a stable thermal behavior during charging and discharging, and a material that does not generate heat due to electrolyte decomposition is used because the charging/discharging potential is stably maintained.

Accordingly, the heat behavior of the coin cell measured by the multi-module calorimeter may be the main cause of the change in cell temperature, such as heat generation of the target electrode, and accordingly, only the thermal behavior of the target electrode can be separated and analyzed.

Specifically, a method for analyzing thermal behavior of individual electrodes according to an embodiment of the present invention comprises: manufacturing a coin cell including a target electrode and a counter electrode; And measuring the thermal behavior of the coin cell by putting the coin cell into a multi-module calorimeter and injecting a current.

First, a coin cell including a target electrode and a counter electrode is manufactured (step 1).

The coin cell may include a target electrode, a counter electrode positioned opposite the target electrode, a separator interposed between the target electrode and the counter electrode, and an electrolyte.

The target electrode may be used without particular limitation as long as it can be used as an electrode for a secondary battery, and may be, for example, a positive electrode including a nickel cobalt manganese (NCM)-based positive electrode active material or a graphite-based negative electrode.

For example, the NCM-based positive electrode active material may include a lithium composite metal oxide represented by Formula 1 below.

[Formula 1]

Li _(1+a) (Ni _(1-abcd) Co _b Mn _c M _d ) On

In Formula 1, 0≤a≤0.5, 0≤b≤1, 0<c≤1, 0<d≤1, 0<a+b+c+d≤1, n is an integer of 2 or 4, M is W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, In, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, And it includes at least one doping element selected from the group consisting of Mo.

In Formula 1, the NCM-based positive electrode active material is W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, In, La, Sr, Ga, Sc, Gd, Sm, Ca , Ce, Nb, Mg, B, and Mo may be doped with any one or two or more doping elements (M) selected from the group consisting of, and when doped with the doping element (M), the active material itself Structural stability can be further improved. In addition, the doping element (M) may be included in an amount of 2000 ppm or less based on the total weight of the positive electrode active material, but is not limited thereto.

The counter electrode is made of a material having a stable thermal behavior during charge and discharge, and a charge/discharge potential is maintained stably so that heat generation due to decomposition of an electrolyte during charge and discharge does not occur.

The counter electrode may specifically include an active material selected from the group consisting of lithium iron phosphate (LFP) and lithium titanium oxide (LTO), but is not limited thereto.

For example, when an electrode containing an LFP-based active material is used as the counter electrode, the electrode containing the LFP-based active material has an olivine structure and is structurally stable because it has a stable oxidation state. It maintains a flat potential and does not generate heat due to electrolyte decomposition. When an electrode containing an LTO-based active material is used as the counter electrode, the electrode containing the LTO-based active material has a spinel structure, and there is no change in volume because electrolyte decomposition is not repeated during charge and discharge, and the operating potential is about 1.5 V. However, since it is not as low as lithium, there is no significant electrolyte decomposition, and there is no deterioration in performance due to changes in film properties, so it is structurally stable.

The LFP-based active material may include a compound represented by Formula 1 below, and the LTO-based active material may include a compound represented by Formula 2 below.

[Formula 2]

Li _1+a1 Fe _1-x1 M _x1 (PO _4-y1 )X _y1

[Formula 3]

Li _x2 Ti _y2 O _{12 -z2}

In Formulas 2 and 3, M is at least one element selected from the group consisting of Al, Mg, Ni, Co, Mn, Ti, Ga, Cu, V, Nb, Zr, Ce, In, Zn and Y, and X Is one or more elements selected from the group consisting of F, S, and N, and -0.5≤a1≤0.5, 0≤x1≤0.5, 0≤y1≤0.1, 0.5≤x2≤4, 1≤y2≤5, 0≤ z2≤9.

Specifically, the electrode including the LFP-based active material may be LiFePO ₄ , and the electrode including the LTO-based active material is Li ₄ Ti ₅ O ₁₂ , Li ₂ TiO ₃ , Li ₂ Ti ₃ O ₇ , and It may include a compound selected from the group.

Meanwhile, the counter electrode may be an electrode in a charged state or a discharged state in addition to the bare state. Using the counter electrode as an electrode in a charged state or a discharged state is that if the target electrode exhibits a reaction to release lithium during the charging process, the counter electrode must be able to exhibit a reaction to accept lithium. If the initial state is a state that cannot accept lithium, it must be made into a state that can accept lithium (discharged state). Conversely, if the metabolic electrode exhibits a reaction that accepts lithium during the charging process, the counter electrode must be able to exhibit a reaction that releases lithium. Therefore, if the initial state of the counter electrode is a state that cannot release lithium, it can release lithium. It must be made into a state (charged state) and used.

The counter electrode in the charged state may be obtained by charging the lithium half cell after preparing a test lithium half cell including the counter electrode, for example, to obtain a delivered electrode. And can be used as a counter electrode.

The counter electrode in the discharged state may be obtained by discharging the lithium half-cell after preparing a test lithium half-cell including the counter electrode, for example, to obtain a litiated electrode, and the counter electrode Can be used as

In one embodiment of the present application, in the case of separating and analyzing the individual thermal behaviors of the positive electrode and the graphite-based negative electrode including the NCM-based active material, respectively, the following coin cells were prepared, and the positive electrode and the black electrode including the NCM-based active material The individual thermal behavior of the linked cathode can be isolated and analyzed.

For example, when separately analyzing the individual thermal behavior of a positive electrode containing an NCM-based active material, a target electrode containing an NCM-based active material is used as the target electrode, and a counter electrode containing an LTO-based active material or charged A counter electrode including an LFP-based active material may be used. At this time, the cell voltage of the manufactured coin cell is 2.1 V to 2.8 V in the case of the NCM/LTO coin cell, and 0.2 V to 0.9 V in the case of the NCM/charged LFP coin cell.

For example, when analyzing the individual thermal behavior of a graphite-based negative electrode, a graphite-based negative electrode is used as a target electrode, and a counter electrode containing an LFP-based active material or a counter electrode containing a discharged LTO-based active material is used as the counter electrode. Can be used. At this time, the cell voltage of the manufactured coin cell is from 3.4 V to 3.6 V in the case of a graphite/LFP coin cell, and from 1.3 V to 1.5 V in the case of a graphite/discharged LTO coin cell.

The coin cell including the target electrode and the counter electrode may further include at least one stacked structure in the structure. This is to maximize the amount of heat generated during MMC analysis. To this end, when using the same charging and discharging equipment, the lower the voltage of the combination of the target electrode and the counter electrode forming the series connection, the more the number of coin cells that can be connected in series in the cell can be increased. Can be maximized.

For example, when using a charging/discharging equipment operating in the range of 0 to 10V, in the case of the NCM/LTO coin cell, 1 to 4 coin cells can be connected in series, and in the case of the graphite/LTO coin cell One or two coin cells can be connected in series, and in the case of the NCM/charged LFP coin cell, 1 to 10 coin cells can be connected in series, and in the case of the graphite/discharged LTO coin cell One to six coin cells can be connected in series.

In addition, when the coin cell manufactured as described above is overcharged, even if the SOC (state of charge) change of the counter electrode is large, it is necessary to adjust the N/P ratio between the target electrode and the counter electrode so that the counter electrode can maintain the potential. Can include. The N/P ratio of the target electrode and the counter electrode can be controlled by adjusting the electrode loading amount of the cell to be manufactured. For example, in the case of an NCM/LTO coin cell and an NCM/filled LFP coin cell, the N/P ratio of the target electrode and the counter electrode is preferably 2 or more, specifically 2 to 3, and graphite/LTO coin cell and In the case of a graphite/discharged LTO coin cell, 0.5 or less, specifically 0.2 to 0.5 is preferable. By adjusting the N/P ratio of the target electrode and the counter electrode to the above range, it is possible to effectively remove the thermal behavior of the counter electrode during the thermal behavior test while maintaining the flat section range of the counter electrode. The accuracy of the behavior measurement can be improved. The N/P ratio between the target electrode and the counter electrode is a value set under the condition that the overcharge test starts at 100% SOC based on the cell capacity and ends at about 200% SOC. As the evaluation SOC range increases, the target electrode and the relative The electrode's N/P ratio can also be changed.

Each of the target electrode and the counter electrode may optionally further include a conductive material and a binder.

Specifically, the binder is polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene , Polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluorine rubber, and various copolymers.

The conductive material is not particularly limited as long as it has conductivity without causing a chemical change in the battery, for example, graphite; Carbon-based substances such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black; Conductive fibers such as carbon fibers and metal fibers; Metal powders such as carbon fluoride, aluminum, and nickel powder; Conductive whiskey such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives may be used.

On the other hand, the separator is a conventional porous polymer film used as a separator, for example, polyolefin such as ethylene homopolymer, propylene homopolymer, ethylene/butene copolymer, ethylene/hexene copolymer, and ethylene/methacrylate copolymer. A porous polymer film made of a polymer-based polymer may be used alone or by stacking them, or a non-woven fabric made of a conventional porous non-woven fabric, such as a high melting point glass fiber or polyethylene terephthalate fiber, may be used, but is limited thereto. It is not.

In this case, in order to secure heat resistance or mechanical strength, an organic-inorganic composite separator coated with an inorganic material may be used, and optionally, a single layer or a multilayer structure may be used.

The inorganic material is not particularly limited and may be used as long as it is a material capable of uniformly controlling the pores of the organic-inorganic composite separator and improving heat resistance. For example, non-limiting examples of the inorganic material include SiO ₂ , Al ₂ O ₃ , TiO ₂ , BaTiO ₃ , Li ₂ O, LiF, LiOH, Li ₃ N, BaO, Na ₂ O, Li ₂ CO ₃ , CaCO ₃ , LiAlO ₂ , SrTiO ₃ , SnO ₂ , CeO ₂ , MgO, NiO, CaO, ZnO, ZrO2, SiC, and at least one selected from the group consisting of derivatives thereof and mixtures thereof.

The average diameter of the inorganic material may be 0.001 µm to 10 µm, more specifically 0.001 µm to 1 µm. If the average diameter of the inorganic material is within the above range, dispersibility in the coating solution is improved, and the occurrence of problems in the coating process can be minimized. In addition, not only can the physical properties of the final separation membrane be uniform, but inorganic particles are evenly distributed in the pores of the non-woven fabric to improve the mechanical properties of the non-woven fabric, and the size of the pores of the organic-inorganic composite separation membrane can be easily adjusted. There is this.

The average pore diameter of the organic-inorganic composite separation membrane may range from 0.001 µm to 10 µm, and more specifically, from 0.001 µm to 1 µm. When the average diameter of the pores of the organic-inorganic composite separator is within the above range, gas permeability and ionic conductivity can be controlled to a desired range, and when a battery is manufactured using the organic-inorganic composite separator, the contact between the positive electrode and the negative electrode is It can eliminate the possibility of a short circuit inside the battery.

The porosity of the organic-inorganic composite separator may be in the range of 30% by volume to 90% by volume. When the porosity is within the above range, ionic conductivity increases and mechanical strength may be excellent.

The electrolyte may include, but is not limited to, an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel polymer electrolyte, a solid inorganic electrolyte, and a molten inorganic electrolyte that can be used when manufacturing a secondary battery.

Specifically, the electrolyte may include an organic solvent and a lithium salt.

The organic solvent may be used without particular limitation as long as it can serve as a medium through which ions involved in the electrochemical reaction of a battery can move. Specifically, examples of the organic solvent include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; Ether solvents such as dibutyl ether or tetrahydrofuran; Ketone solvents such as cyclohexanone; Aromatic hydrocarbon solvents such as benzene and fluorobenzene; Dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), propylene carbonate, Carbonate-based solvents such as PC); Alcohol solvents such as ethyl alcohol and isopropyl alcohol; Nitriles, such as R-CN (R is a C2-C20 linear, branched or cyclic hydrocarbon group, and may contain a double bonded aromatic ring or an ether bond); Amides such as dimethylformamide; Dioxolanes such as 1,3-dioxolane; Alternatively, sulfolanes or the like may be used. Among them, carbonate-based solvents are preferable, and cyclic carbonates having high ionic conductivity and high dielectric constant (e.g., ethylene carbonate or propylene carbonate, etc.), which can increase the charging/discharging performance of the battery, and low-viscosity linear carbonate-based compounds ( For example, a mixture of ethylmethyl carbonate, dimethyl carbonate or diethyl carbonate) is more preferable. In this case, when the cyclic carbonate and the chain carbonate are mixed in a volume ratio of about 1:1 to about 1:9, the electrolyte may exhibit excellent performance.

The lithium salt may be used without particular limitation as long as it is a compound capable of providing lithium ions used in lithium secondary batteries. Specifically, the lithium salt is LiPF ₆ , LiClO ₄ , LiAsF ₆ , LiBF ₄ , LiSbF ₆ , LiAl0 ₄ , LiAlCl ₄ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiN(C ₂ F ₅ SO ₃ ) ₂ , LiN(C ₂ F ₅ SO ₂ ) ₂ , LiN(CF ₃ SO ₂ ) ₂ . LiCl, LiI, or LiB(C ₂ O ₄ ) ₂ or the like may be used. The concentration of the lithium salt is preferably used within the range of 0.1 to 2.0M. When the concentration of the lithium salt is within the above range, since the electrolyte has an appropriate conductivity and viscosity, excellent electrolyte performance can be exhibited, and lithium ions can effectively move.

In addition to the electrolyte constituents, the electrolyte includes, for example, haloalkylene carbonate-based compounds such as difluoroethylene carbonate, pyridine, and trivalent for the purpose of improving battery life characteristics, suppressing reduction in battery capacity, and improving battery discharge capacity. Ethyl phosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexaphosphate triamide, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N,N-substituted imida One or more additives, such as zolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxy ethanol, or aluminum trichloride, may be further included. At this time, the additive may be included in an amount of 0.1 to 5% by weight based on the total weight of the electrolyte.

Next, the coin cell is placed in a multi-module calorimeter, and current is injected to measure the thermal behavior of the coin cell (step 2).

The multi-module calorimeter measures the temperature behavior of a battery under adiabatic conditions. Specifically, it is possible to measure the thermal behavior of the coin cell while overcharging by inserting a coin cell into the multi-module calorimeter and injecting current. In this case, the amount of current injected into the coin cell may vary depending on the loading amount of the target electrode and the counter electrode constituting the coin cell.

In addition, it may be to inject current into the coin cell and overcharge the coin cell. The'overcharge' refers to charging a fully charged coin cell with 100% SOC with 200% SOC. Specifically, the coin cell may be overcharged by continuously injecting current into the coin cell until the SOC reaches 200%.

As described above, since the charge/discharge potential of the counter electrode included in the coin cell is stably maintained during charging and discharging, heat generation due to decomposition of the electrolyte solution does not occur during overcharging. Accordingly, the thermal behavior measured in step 2 is the main cause of the change in the thermal behavior of the target electrode, and accordingly, only the thermal behavior of the target electrode may be separated and analyzed.

Claims (12)

Manufacturing a coin cell including a target electrode and a counter electrode; And,
Putting the coin cell into a multi-module calorimeter and injecting current to measure the thermal behavior of the coin cell
The counter electrode includes an active material selected from the group consisting of lithium iron phosphate (LFP) and lithium titanium oxide (LTO).
delete The method according to claim 1,
The coin cell is a method of analyzing the thermal behavior of individual electrodes comprising a target electrode including a nickel cobalt manganese (NCM)-based active material and a counter electrode including an LTO-based active material.
The method of claim 3,
The cell voltage of the coin cell is 2.1 V to 2.8 V, the method of analyzing the thermal behavior of individual electrodes.
The method according to claim 1,
The coin cell is a method of analyzing the thermal behavior of individual electrodes comprising a target electrode including an NCM-based active material and a counter electrode including a charged LFP-based active material.
The method of claim 5,
The cell voltage of the coin cell is 0.2 V to 0.9 V, the method of analyzing the thermal behavior of individual electrodes.
The method according to claim 1,
The coin cell is to include a graphite target electrode and a counter electrode including an LFP-based active material, the thermal behavior analysis method of the individual electrode.
The method of claim 7,
The cell voltage of the coin cell is 3.4 V to 3.6 V, the method of analyzing the thermal behavior of individual electrodes.
The method according to claim 1,
The coin cell includes a graphite target electrode and a counter electrode including a discharged LTO-based active material.
The method of claim 9,
The cell voltage of the coin cell is 1.3 V to 1.5 V, the method of analyzing the thermal behavior of individual electrodes.
The method according to claim 1,
The coin cell is a method of analyzing the thermal behavior of individual electrodes comprising a structure connected to one or more layers.
The method according to claim 1,
The measuring of the thermal behavior is performed by placing the coin cell in a multi-module calorimeter and injecting a current to overcharge the coin cell.